Hot-workable steel with sulfur and vanadium

ABSTRACT

PLAIN CARBON OR ALLOY STEEL HAVING SULFUR IN RESIDUAL OR RESULFURIZED AMOUNTS AND CONTAINING AT LEAST 0.01 WT. PERCENT BUT LESS THAN 0.03 WT. PERCENT VANADIUM, COLUMBIUM, TANTALUM OR COMBINATIONS THEREOF AS GRAIN REFINER. AUSTENITIC GRAIN SIZE AT LEAST AS FINE AS 7 ON ASTM SCALE. SULFUR-CONTAINING INCLUSIONS ALSO CONTAIN OXYGEN, IRON AND MANGANESE, HAVE A GLOBULAR SHAPE AND ARE RANDOMLY DISPERSED THROUGHOUT MICROSTRUCTURE. NO ALUMINUM.

United States Patent Office 3,600,158 Patented Aug. 17, 1971 3,600,158HOT-WORKABLE STEEL WITH SULFUR AND VANADIUM Louis Molnar, Hammond, Ind.,and William E. Heitmann, Dolton, Ill., assignors to Inland SteelCompany, Chicago, Ill. No. Drawing. Filed July 13, 1967, Ser. No.653,039

Int. Cl. C22c 39/50 US. Cl. 75-123 4 Claims ABSTRACT OF THE DISCLOSUREPlain carbon or alloy steel, having sulfur in residual or resulfurizedamounts and containing at least 0.01 wt. percent but less than 0.03 wt.percent vanadium, columbium, tantalum or combinations thereof as grainrefiner. Austenitic grain size at least as fine as 7 on ASTM scale.Sulfur-containing inclusions also contain oxygen, iron and manganese,have a globular shape and are randomly dispersed throughoutmicrostructure. No aluminum.

BACKGROUND OF THE INVENTION Sulfur is present in steel either inresidual amounts or in larger amounts purposely added to impart desiredproperties (such as improved machinability) to the steel.

Sulfur is generally found in steel as a component of a microscopicinclusion also containing iron, manganese and oxygen. Thesesulfur-containing inclusions are in the absence of some interferingmedium, generally globular in shape and are randomly dispersedthroughout the microstructure of the steel.

It is desirable for steel to have a relatively fine austenitic grainsize because this improves the toughness of the steel. A common practicefor refining the grain size of steel is to add a grain refiner; and acommon grain refiner has been aluminum, e.g., in amounts between 0.02and 0.05 wt. percent.

Aluminum is also a deoxidizer and, when added as a grain refiner,substantially reduces the amount of oxygen in the steel. For example, ina steel otherwise normally having 150-200 parts of oxygen per millionparts of iron, grain refining with 0.02-0.05 wt. percent aluminumreduces the oxygen content to less than 50 parts per million parts ofiron.

When aluminum deoxidizes the steel, it substantially eliminates oxygenas a component of the sulfur-containing inclusion; and, when thisoccurs, the shape and distribution of the inclusions change from aglobular shape randomly dispersed throughout the microstructure to astringy shape concentrated at the grain boundaries of themicrostructure.

When a steel has sulfur-containing inclusions concentrated at the grainboundaries of the steel, the hot-working characteristics of the steelare poorer than those of a steel having sulfur-containing inclusionsrandomly dispersed throughout the microstructure.

When a steel has sulfur-containing inclusions with a stringy shape, themachinability of the steel is poorer than that of steel havingsulfur-containing inclusions which are globular in shape.

SUMMARY OF THE INVENTION In accordance with the present invention, thereis provided a steel having a relatively fine austenitic grain size (atleast as fine as 7 on the ASTM scale) together with sulfur-containinginclusions having oxygen as a component. The inclusions are randomlydispersed throughout the microstructure of the steel and have a globularshape.

The steel contains a grain refiner selected from the group consisting ofcolumbium, tantalum, vanadium and combinations thereof, in an amount atleast 0.01 wt. percent and less than 0.03 wt. percent. Aluminum is notused as a grain refiner and no aluminum is present in the steel.Columbium, tantalum, vanadium, or combinations thereof, in the rangespecified in the preceding paragraph, effectively refine the grain sizeof the steel. Lesser amounts would have no significant effect on grainrefinement; and additional amounts would have no significant additionaleffect on grain refinement, compared to an amount, such as 0.02 wt.percent, within the range specified. Because these elements arerelatively expensive, it is important that they not be added in amountsat which no significant additional eifect is produced.

Columbium, vanadium and tantalum are not deoxidizers so that oxygen isnot removed from the steel by these grain refiners, and oxygen ispresent as a component of the sulfur-containing inclusion, along withiron and manganese. Thus, a steel normally containing 150-200 parts ofoxygen per million parts of iron would have the same oxygen content bothbefore and after the addition of a grain refiner in accordance with thepresent invention.

The invention is applicable to all sulfur-containing steels, whether thesulfur is present in residual amounts (e.g. 0.03-0.05 wt. percent) or ispresent in resulfurized amounts purposely added to impart desiredproperties to the steel. An example of the latter is sulfur added toimprove the machinability of the steel, in which case sulfur is added inamounts typically between 0.1 wt. percent and 0.35 wt. percent. Thisinvention is applicable to all types of sulfur-containing base steels,whether the base steel be a plain carbon steel or an alloy steel.

Other features and advantages are inherent in the steel claimed anddisclosed or will become apparent to those skilled in the art from thefollowing detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Illustrative examples of basesteels which may be modified in accordance with the present inventionare tabulated below. The examples include a plain carbon steel havingresidual amounts of sulfur (AISI 1040), a plain carbon, resulfurizedsteel (AISI 1117) and an alloy steel having residual sulfur (AISI 4142).The respective compositions of these base steels are as follows:

AISI 1040 Each of these base steels may be modified in accordance withthe present invention by adding at least 0.01 wt. percent but less than0.03 wt. percent vanadium, columbium, tantalum or combinations thereof.

For each of the compositions listed above, when modified in accordancewith the present invention, aluminum is not added as a grain refiner andaluminum is not present in the steel. The steel has an austenitic grainsize of 7 or finger on the ASTM scale, the austenitic grain size beingdetermined by the conventional McQuaid-Ehn grain size test.

The sulfur-containing inclusions in these steels have a globular shapeand are randomly dispersed throughout the microstructure of the steel.The sulfur-containing inclusions also include iron, manganese andoxygen.

In the AISI 1117 steel, sulfur has been added to improve themachinability thereof. The machinability of a steel may also be improvedby including selenium and/ or tellurium in amounts between 0.02-0.10 wt.percent; and neither the machinability nor the hot-workingcharacteristics of such a steel are adversely effected by using a grainrefiner in accordance with the present invention, compared to the use ofaluminum as a grain refiner.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

1. In a steel having sulfur-containing inclusions:

at least 0.01 wt. percent and less than 0.03 Wt. percent of a grainrefiner selected from the group consisting of columbium, tantalum,vanadium and combinations thereof;

said grain refiner being present in an amount sufiicient to produce anaustenitic grain size in said steel at least as fine as 7 on the ASTMscale;

said steel being devoid of aluminum;

said sulfur-containing inclusions also containing oxygen;

said sulfur-containing inclusions having a globular shaped and beingrandomly dispersed throughout the steel.

2. In a steel as recited in claim 1 wherein the sulfur content is atleast a residual amount and up to 0.35 wt. percent.

3. In a steel as recited in claim 2 wherein said sulfur content is atleast 0.1 wt. percent.

4. In a steel as recited in claim 1 wherein said inclusions consistessentially of iron, manganese, sulfur and oxygen.

References Cited UNITED STATES PATENTS 2,158,652 5/1939 Becket 75-1232,168,561 8/1939 Critchett 75l23X 2,182,758 12/1939 Harder 751232,157,673 5/1939 Ridgely 75-123 2,272,277 2/1942 Ramsey 75-123 3,254,9916/1966 Shimmin 75l23X 2,501,138 3/1950 Parker 75129 2,236,479 3/1941Harder 75l23X 2,236,716 4/1941 Morris 75123 2,258,604 10/1941 Gagnebin7558 3,169,857 2/1965 Rathke 75123 CHARLES N. LOVELL, Primary Examiner

